Pulse recording apparatus



Jan. 13, 1953 J. P. ECKE'RT, JR., ET AL 2,625,607

PULSE RECORDING APPARATUS Filed May 27. 194s 1"@ sheets-smet 1 IN V EN TRS JOHN PRESPER ECKERT JR. JOHN CLARK SIMS JR.

HE ERT FRA En wELsH ArloRNEYs FIG. IA

Jan. 13, 1953 Filed May 27. 1948 J. P. ECKERT, JR.; ETAL PULSE RECORDING APPARATUS 6 Sheets-Sheet 2 ir I -r L@ a E 1 mw N S\ I N n m 1 l 23 N g INVENTORS. JOHN PRESPER ECKERT JR. JOHN CLARK SIMS JR.

ATTORNEY FIG.\B

Jan. 13, 1953 J. P. ECKERT, JR., ETAL 2,625,607

PULSE RECORDING APPARATUS Filed May 27. 1948 6 Sheets-Sheet 3 FIG. 2

IN V EN T ORS.

JOHN PRESPER ECKERT JR.

JOHN CLARK sms JR.

HT FRA WELSH BY t! ATTORNEYS s sheets-sheet 4 N m Fg IN VEN TORS JOHN PRESPER ECKERT JOHN CLARK SIMS JR. HERBT FRAZE WELSH BY 4r r ATTORNE J. P. ECKERT, JR., ETAL PULSE RECORDING APPARATUS iv. NON

m. 7 5 STR H R 1 m, m n@ 5 2 n m O m mmm m 6, wmv o mRsz 2 o3 Ev mi. mmv EKM N h E? SRF Y s 0E MMT T e lnlaall 3v PCR T Nov )s n? NN A n n m HH M 28 o'os l m/ www T x \n n d En m f 4, I R., m c., m @IQH M m IF R M //^m\ ovm 0mm E R .K Mw m m m P, w. J vP .w .O L 3 3 E w Mw 7. om #Nm f 3, w vom non n n o m mmm l M n. w a n.. J F

Jan. 13, 1953 J. P. ECKERT, JR.,A ETAL 2,625,607

PULSE: REcoRmNG APPARATUS Filed May 27. 194e ,s sheets-sheet e FIG. 8.

IN V EN TR` JOHN PRESPER ECKERT JR.

JOHN CLARK SIMS JR.

HERZ: FRAzE WELSH BY l f-rv ATTORNEYS Patented Jan. 13, 1953 PULSE RECORDING APPARATUS John Presper Eckert, Jr., John C. Sims, Jr., and

Herbert Frazer Welsh, Philadelphia, Pa., assignors to Eckert-Mauchly Computer Corporation, Philadelphia, Pa., a corporation of Penn- Sylvania Application May 27, 1948, Serial No. 29,434

31 Claims. 1

This invention relates to magnetic or similar recording apparatus and has particular reference to the recording of information on magnetic tape in coded form and the reproduction of such information from the tape through a relatively slowly acting mechanism such as an electrical typewriter. While certain aspects of the invention relate to the use of magnetic tape containing a plurality of recording channels, other aspects could equally relate to magnetic wire recording and reading. For simplicity of description tape will be referred to with the understanding that this term includes wire wherever the invention would be applicable thereto, i. e., not necessarily directed to multiple channel operations.

In devices for reading out information recorded magnetically on tapes, as in sound reproducing systems, it is customary to move the tape relatively to a pick-up unit at such a high rate of speed that the electrical output from the pick-up unit is in the form of a suiiiciently high frequency electric potential or current, and of suiiicient magnitude above background noise, that amplification is readily effected to operate either a sound reproducer or other devices which are adapted to make use of the relatively high frequency output. Heretofore, magnetic tape recording has been useful only when used in systems in which such a high frequency output can be utilized. Magnetic tapes, however, are well adapted for the storage of coded information in the way of minute magnetized spots thereon which, for convenience of terminology, will be hereinafter referred to as pulses; for example, as

y indicated hereafter a magnetic tape may very well be provided with multiple lengthwise channels carrying pulses selectively arranged so that a particular combination of pulses existing in vcorresponding positions in the various channels may represent numbers, letters, punctuation, machine instructions or other information. In most instances, however, the information thus carried by a tape cannot be utilized at the rate of delivery of the information through a pick-up head cor- 1 responding to such lineal` speeds of the tape as would give rise to output signals of a magnitude which could be amplified and utilized. As an example, suppose it is desired to use the tape to `control an electric typewriter. In such a case the information which may determine the printing by a particular key of the :typewriter may be represented by pulses having a length along the tape of no more than, say, ten thousandths of an inch, and for conservation of the tape the l particular arrays of pulses representing different characters to be typed would not be spaced more than a few thousandths of an inch along the length of the tape. If the typewriter is to be operated from the output of the pick-up without the interposition of intermediate memory devices, it is obvious that the speed of the tape must be correlated with the typing speed of the typewriter which may mean, for example, that no more than sixteen characters should be delivered by the tape pei` second. This would represent a very slow movement of the tape at a rate,.at most, of only a fraction of an inch per second with. the result that only extremely small signals would be obtained from the pick-up, quite impractical to segregate from background noiseat an amplifier output. 1

It is one object of the present invention to provide means for reading information fromja Vmagnetic tape when the tape is essentially stationary or moving very slowly so far as its average y speed of advance is concerned. Brieiiy stated,

this result is secured, in a preferred embodiment of the invention, by imparting to the tape in the vicinity of a pick-up a rapid vibration of quite small amplitude so as to get an output signal involving a modulated carrier having the frequency of the vibration, the modulation depending upon the pulses on the tape. In accordance with the invention, however, other modulationmethods may be used though, generally speaking, they are inferior in involving the necessity for avoidance of disturbing effects produced by the earths magv netic eld or other stray magnetic fields.

It will be evident that by thus producing a modulated carrier information may be read from the tape as slowly as may be desired from the standpoint of the frequency of succession of the units of information and hence the invention is applicable for the direct drive, without intermediate memory devices, of such mechanisms as typewriters or other printing apparatus or of card or tape punches or the like.

One of the broad objects of the present invention is concerned with the attainment of slow reading out of information in the fashion indicated.

A further object of the invention relates to the provision of means for making use of the modulated carrier of the type described. As will be evident, when the information is carriedv by a tape on a plurality of channels, the response of an ultimate device, such as a typewriter,.must be determined by what is picked up from some points bearing a predetermined relationship with each other in the several channels. If conservation of the tape is to be achieved with very close spacing of the units of information along the length of the tape it will he obvious that extreme and practically unattainable accuracy of mechanicalparts would be required toy insure that corresponding modulations of `the various carrier channels should be so precisely in phase as to exercise their results practically simultaneously.V

Another object of the present invention is, therefore, to provide a system which Vwill `insure the proper utilization of the signals delivered from a group of pick-ups to avoid reading errors while nevertheless permitting the maximum amount of information to be carried per unit length of the tape.

As will be evident from the detailed description hereafter, the attainment of thelast mentioned object solves not only the problem of securing proper pick-up of signalsfrom a number of channels of a slowly moving tape but also that of securing froma number of channels of a rapidly moving tape a number of substantially simultaneous `signals despite'ina'ccuracy of alignment of signals in the individual channels With their respective heads. Hence this last mentioned object is not limited to the use of a slowly moving tape; furthermore it is not limited to a modula- 'tion system.

A further objectofv the invention'is to provide apick-up'unit which will insure as nearly as pos- .siblesimultaneous delivery from a tape of'signals 'which should theoretically be delivered simulta- Vinvolved'in reading the information from the tape thus leading to simplicity in a system which, in `its entirety, permits storing of information on the tape bymanipulation of a typewriter and reproduction from the tape on the same or a similar typewriter or on a battery of similar typewriters.

Particularly 'it is an object of the invention to provide recording .and pick-upassemblies of such type 'as to make easy precise duplication of construction so that tape records made on one mechanism may be read on another with assurance of accurate reproduction of the original recorded information. It will be obvious that certain aspects of the invention are applicable to recording on, .and reproduction from, nlms or .tapes .on whichrecordingis eifectedphotographically or by printing or other process rather than magnetically.

.Itis further object of theinvention to provide means for recording and reading .out information to .orfrom a number of very closely arranged channels on a tape without cross-talk during either recording or reproduction.

Another object of the invention relates to an improved means for securing modulated signals from a tape by causing vibration of the tape locally.

As will be later evident, some of the objects above are not limited to the reading of or recording on magnetic tape: but are applicable to other types of reading and recording involving, for example, photographi-c nlm, perforated tape or the like.

vThese and other objects of the invention particularly relating to details of construction and operation will become apparent from the following 'description read in conjunction with the accompanying drawings in which:

Figures 1A and 1B are complementary Wiring diagrams illustrating the wiring of the apparatus but involving, as shown, only the apparatus for a single channel together with those parts which are common to a complete group of channels;

Figure 2 is a block diagram which, considered in conjunction with Figures 1A and 1B, will make clear the fashion in which control is effected in the use of multiple channels;

Figure 3 is an inverted plan View, partially in section, of a magnetic head unit used for both recording and reproduction;

Figure 4 is an end elevation of the same;

Figure 5 is aside elevation of the same;

`Figure 6 .is a. transverse section taken on the plane indicated at -i in Figure 3;

Figure? is a .fragmentary sectional view illustrating' the construction of a single head;

Figure 8 is an elevation, partly diagrammatic in character, illustrating a magnetic tape feeding device, together with the means for vibrating a portion of the tape in the direction of its length; and

Figure 9 is a sectional view illustrating certain switching elements of a conventional electrical teletypewriter.

rihere will be first considered Figures 1A and 1B which illustrate the electrical details and interconnections of four types of elements, A, B, C and D which are bounded by the rectangles correspondingly designated. A represents what might be called an amplifier and phase detector element. B is a power amplier involving a nipflop which serves the purpose of providing a memory and holds the pulse or no-pulse condition of the read-in signal from a tape during the time that other channels are setting up in preparation for the parallel reading out from all channels. C is a timing and control element. D is a signal generator. Only one unit C and one unit D are included in a complete system. Of the eiements A. and B, however, there is one of each corresponding to'each tape channel which is connected to the key and type mechanism of an electrical typewriter. For consistency of description it will be assumed that there are six such channels though the magnetic tape may contain additional channels utilized to carry control information; in fact, in Figures 3 to 7, inclusive, provision for eight channels is illustrated. Reference will be later made to Figure 2 to show how the elements which occur in multiple are connected into the system; Figures 1A and 1B, however, show in detail only one element A and only one element B which would correspond .to the same tape channel.

The coil of the recording and reproducing head of a channel is indicated at 2, As will be pointed out hereafter the same head is used for both purposes and references to recording and reproducing will be used only to distinguish the functions of the head directly under consideration. One of the terminals l of the coil 2 is connected to a line 5 which constitutes a common line for the corresponding terminals of all of the head coils. During reproduction this line is connected to zero potential; during recording it is connected to a positive 220 volt source. The other terminal 3 of the coil is connected to a single-pole double-throw switch 'i which may selectively connect it to contacts S and It. In the figures under discussion there are a number of double-throw switches illustrated and for consistency all of these switchesare illustrated in the positions which they occupy when reading of the tape is to be eiected,

As illustrated, the coil 2 is connected to the primary of the input transformer I2, the secondary oi which is tuned by a condenser I4 to the standard frequency of the system, i. e., that frequency at which the tape is oscillated. Signals from the tuned secondary are passed through condenser iS to the control grid of a pentode ampliiier tube i8, there being provided a conventional grid resistor 29 and plate load resistor 26 with conventional screen supply. Connected to the cathode is a iixed bias resistor 28 bypassed by a condenser 30, this resistor being in series with a potentiometer 32 which is part of a feed-back arrangement mentioned hereafter. The output from the plate of tube i8 passes through the condenser 3d to the control grid of a second pentode 36 having the conventional grid resistor 3B, a cathode biased resistor 45 bypassed by condenser 48 and conventional screen and plate connections, the plate resistor being shown at 59. The output from this stage is delivered through the condenser 5i to the grid of the triode 52 in a cathode follower circuit. VThe triode 52 has its grid resistor 54 connected to the junction of the cathode resistors 56 and 5B across which the signal is developed, The cathode current of this tube flows back through the line 6i! and a portion of the potentiometer 32 so that there is developed a potential in the cathode circuit of the tube i8 providing inverse feedback to insure uniform gain characteristics of this amplier system. Without such inverse feedback the amplifier would change its operating characteristics as the tubes and other components of the circuit age.

At this point it may be remarked that, to facilitate understanding of the operation by those skilled in the art, there are indicated at various terminals the direct potentials provided by a conventional power supply, the details of which need not be considered since they are well konwn; for example, it will be noted that the plate and screen potentials of the amplifying system so far described are provided from a direct positive 210 volt source while the lower end of the potentiometer 32 is connected to a Zero voltage point in the system.

The amplified signal from the three stage amplifier which has been described is delivered through the condenser 52 to the grid circuit of the triode 64. The signals developed by the amplier are sufliciently large to drive the tube Gill from below cut-oil well into saturation. The grid circuit of the tube d4 includes two resistors t6 and 53. The resistor 66 is such that when the output signal from the amplifier drives the grid tri positive the grid current now through resistor S6 will provide a potential drop so as to prevent the grid from going substantially positive relative to its cathode. The peak of the wave is thus clipped. It will be noted that the resistor 68 is returned to a potential of minus 70 volts, suiiiciently lower than its cathode potential of minus 60 volts so that the triode 54 is completely cut off when no signals are delivered to it. The purpose of the triode 54 and its circuit is to transform approximately sinusoidal waves at the input of the amplifier into pulses of approximately rectangular shape in the output from the triode The use of the large negative bias on the grid of triode 54 inhibits operation of the triode until certain minimum signals have been delivered to it and thus it suppresses noise signals which may come through the amplifier but which are of less than a critical amplitude. The pulse-like signals produced in the triode 64 appear across the resistor w which connects the plate of this triode with a positive volt potential. It may be noted that the arrangement described not only produces substantially rectangular pulses but pulses which are also relatively narrow as compared with the half period of a substantially sinusoidal input.

These narrow pulses are fed to a diode gating circuit providing phase detection. To the plate of triode 64 are connected the anodes of diodes l2 and l, which (as well as other diodes indicated hereafter) may be of the germanium crystal type, in series with respective resistors I6 and 18 which have a common return to the negative '70 volt potential source for the grid of triode 64. (It may be here noted that, throughout the drawings, the arrow heads in diodes indica-te their cathodes while 4the orthogonal lines indicate their anodes.) When no signal or a negative signal is delivered to the triode its grid will be in cut-off condition and its plate, in the absence of the diodes and their connections, would rise to the plus 85 volt potential to which the plate resistor 1B is connected. However, since the diodes are connected through their resistors to the negative potential source they will be conducting and the current iiow through `the resistor 'it will decrease the maximum potential to which the plate of triode 5t may rise by reason of the drop through resistor l5. Although the return is to a negative 7G vol-t potential, under these conditions of zero or negative signal to the grid or triode 64 the cathodes o1" the diodes 'l2 and 74 will be at a positive potential with respect to the zero reference potential, the resistors lu, l@ and T8 having values to secure this condition consistent with the total current ows therein.

If the circuit so far described up to and including the triode iid is examined it will be noted that a positive swing of the control grid of the tube i8 will produce a negative pulse at the anode of the triode 64. These negative pulses have their peaks below the zero of potential and if it were not for additional current flow to the cathodes of the diodes 'I2 and 'Iii their cathodes would be rendered negative by reason oi the connections through the resistors 'I6 and i3 to the negative potential source. However, as will be pointed out shortly, this does not occur until a coincidence occurs between a negative pulse at the anode of the triode with negative pulses provided from the signal. generator which will now be described. To complete the description of the element A, however, it may be noted that the cathodes of the diodes l2 and 'I4 are respectively connected through crystal diodes t2 and 8B to lines St and E35. Furthermore, they are respectively connected through the series arrangement of diodes S8 and ESS, and 88 and respectively, to the lines H22 and 92. In addition, the cathode of the diode l2 is connected through the crystal diode $56 to the line ii. .it will be noted that in all of these cases the cathodes are connected together. The various lines just mentioned will reappear hereafter.

Sl'he signal generator indicated at D consists of an oscillator tilt which may be of any suitable type but which is illustrated as of the Colpitts type. This consists of a triode Hi8 having a plate resistor HB connected to a positive potential source. Signals appearing across this plate Yresistor'are ied backto the grid circuit through anginductor 1||2in Vseries with a condenser I I6, vboth beinggshunted by the condenser H4. From the junction point H8 connection is made through the condenser |23 to the grid of the `triode |08, there being provided the usual grid resistor |22. This oscillator operates in conventional fashion to provide an output at the frequency at which it is desired to oscillate the `tape from'which signals are being read.

The output from the plate circuit of the oscillator is fed through blocking condenser |2Li to the grid of the triode |2 which acts as a phase inverter. This triode has a suitable grid resistor |28 connected to lthe junction of the two cathode resistors |30 and |32. These two cathode resis- ,tors have a total Vseriesresistance approximately equal to the resistance of plate resistor i3d and thus the signal developed across the resistor |34 is approximately equal to that developed across Vthe series arrangement of the resistors i3@ and |32. The signals, however, will be 180 out of phase with each other. These signals are fed through blocking condensers |35 and i3d to the control grids of the triodes Edil and IGZ which act as power amplifiers. The input resistors ldd and |45 of these tubes are returned to Zero potential While the cathodes of the tubes Idil and |i2 are returned to zero potential through a common bias resistor |58. The plates of the two tubes ld and Id are connected in push-pull to an output transformer |53 in the manner normally used for audio power drive. The secondary |52 of the transformer |553 is matched with and connected to the tape oscillating driver as will be described hereafter, the connection of this being to the terminals |53 and |55 of the transformer secondary. It will be noted that the terminal |55 is groundedl The terminal |53 is connected through the line |51 to a phase shifter comprising the variable resistor |55 and the condenser |58. The purpose of this phase shifter is to produce a shift in phase to compensate for any phase shift which may occur in the electromechanical device which oscillates the tape to insure coincidence of pulses as later described. Signals are fed from the phase shifter through blocking condenser |66 and resistor |62 to a conventional flip-nop iii-i of the Eccles-Jordan type which is well known in the art. Resistor |62 is present to avoid interference by condensers |58 and l5@ with the flipping action. High speed operation is not here required and hence the flip-flop can be of the type suitablefor low speed operation. The output of the nip-flop delivered through the condensers |541 and |66 will consist of square waves occurring at the frequency of the oscillator H56, but as delivered through the two condensers, 180 out of phase with each other. These condensers are connected to a pair of resistors Hi8 and |1, the junction point of which connects with a negative '10 volt potential source. The signals through the eenden-sers are transmitted to the grids of a pair of triodes |16 and |18 through resistors |12 and |115. The plates of these triodes are connected to a positive 210 volt source through the resistors |89 and |82. The condensers |013 and |66 in conjunction with the resistors |68 and perform differentiation upon the square wave signals, i. e., their time constant is Very short. Pulses will, therefore, be delivered to the grids of the triodes Ilia` and |18 at the times the flipflop |55 undergoes transition. Both tubes |10 vand. |18 are biased to cut-oir and accordingly only positive pulses Vapplied to their grids will be eifective. Thus at the time of zero phase positive peaks, a positive pulse will be delivered to the grid of the tube |18 through the condenser I 646, At the time of the peaks which are 180 out of phase a positive pulse will be delivered to the grid of the tube |16. These positive pulses applied to the grids produce negative pulses at the plates due to currents through the plate resistors and |82. The potential to which the plates of the tubes |1o` and |13 may rise at the times when their grids are cut-off is limited by the presence of the crystal diodes ld and |83 which have a return `to a positive 10 volt potential source. Negative pulses Qriginatingjfrom va posi- .tive v10 volt origin are, therefore, delveredto `,the linesd and 86.

I t is now possible to describe the gatingaction c0115 ointly effected by the elements A and D which have so far been described. When no pulsesare provided at the anodes of the crystal diodes 12 and 82 through their respective connections to the Aplate of triode 6 4 and to the line 8S these anodes will be positive and, consequently, current will fiow through the rresistor 'i6 to the negative 70 volt source and their cathodes will be at a positive potential. When a negative pulse emanating from the plate of triode ed is imposed on the anode .of the diode 12 in the absence of a simultaneous pulse through the line 86 the cathode of the diode 12 will be more positive than its anode and, consequently, the diode is, in effect, open-circuited and its cathode takes the approximately 10 volt positive potential of the line 8E. The same action occurs if a negative pulse through the line 6 is not coincident with a pulse from the triode 613, i. e., the junction of thecathodes 4of the diodes 12 and 82 remains positive. A positive condition at this junction involves a positive condition of the cathodes of the crystal diodes 96 and 9S with respect to their anodes and accordingly no outputs will occur through the lines Id or |62.

However, coincidence of negative pulses delivered to the diodes 12 and 82 will remove both sources of positive potentials from their anodes and their cathodes will become negative through connection to the negative '10 volt potential source. Thus negative pulses will be transmitted through the diodes and itil and 98 to the lines Iil and |02. As will be hereafter described, these lines run to the grids ofr triodes having their cathodes at zero potential.

The above explanation identically applies to the diodes 1d and 8S so that coincidence of jnegative pulses from the plate of triode t@ and the line 8G will produce negative pulses through the crystal diodes 88 and 90 to the line Q2, als-o connected to the grid of a triode having its cathode at zero potential.

In accordance with the phasing assumptions which have beenmade previously a positive signal applied to the grid of tube i8 occurring in zero phase, i. e., with the positive peaks at the terminal |53 will result in the production of a negative pulse through the line 92. On Vthe other hand, if these two signals are out of phase there will occur at the time of a positive pulse at the grid of tube I8 negative pulses in the lines |02 and |04. Summarizing, an in phase condition of the grid of tube I3 and terminal |53 will produce negative pulses in line 92; an out of phase condition of the grid of tube |8 and ter.- minal |53 will produce negative pulses in ,lines H02 and E04. Thus a phase selective system is provided.

Referring now to the circuit element C in Figure 1B, there is illustrated at 290 a flip-flop of Eccles-Jordan type comprising the triodes 292 and 294. During the reading of signals from the tape, switches 2t! and and Ztl are in the positions illustrated. Switch Ztl engages a Contact to join the plate of triode 296 to the grid of triode 202 through resistance 2 it and switch 263. This grid is also joined to the line s2. The grid of triode 204 is connected through resistance 253'5 to the plate of triode 202 and also through the switch 207 to the line m2. Resistors 2&2 and 208 connect the grids to a negative potential. It will be noted that the cathodes of triodes 202 and d are returned to a zero potential. The plate of triode 204 is connected through a neon bulb 216 and a series resistor 2 il to a, positive 125 volt potential. It is also connected through condenser 2li? and resistor 222i to a negative 'J0 volt potential. The junction of the condenser S and resistor 226 is connected through resistor 222 to the grid of triode 224i. rEhe cathode of the triode 224 is connected to a negative 60 volt potential source. Its plate is connected to a positive 10 volt potential source through a resistor 22e. Its plate is also connected to the line 223 which runs to the circuit element B hereafter described.

The anode of triode 22d is connected through the condenser 232, switch 233 and resistor 238 to the grid of triode 23d, the plate of which is connected to the line 225i, extending to the circuit element B, and the cathode of which is at zero potential, a switch 235 in the position illustrated also connecting the line 5 to zero potential.

When a pulse is rst encountered on the magnetic tape by a head l its leading edge produces a signal which at the grid of the tube i8 is 180 out of phase with the output at the terminal |53. Accordingly, negative pulses will be transmitted through the line m2 to the grid of the triode 205i cutting oi this triode and extinguishing the neon bulb 2id by raising the plate potential of this triode to the positive 85 volt potential of its source so that the resulting potential drop of volts across the neon bulb is insuicient to maintain current flow through it. At the same time the triode 202 is rendered conducting. At the time of this transition a positive pulse is emitted .through the condenser 2 I ii. It may be here noted that the first negative pulse delivered through the line ft2 will throw the flip-flop 2st into the state just described and subsequent negative pulses through the line lii2 will be without any action on the flip-nop. As will be evident hereafter, such an initial flipping pulse may originate in any one of a group of heads.

The condenser 2 i8 in conjunction with the resistor 22@ provides a differentiating action so as to deliver a sharp positive pulse through the resistor 222 to the control grid of the triode 225 at the time the positive pulse is delivered through the condenser 2l0 due to the transition of the nip-nop just described. The arrival of this sharp positive pulse at the grid of the tube 221i causes a negative pulse to be developed at its plate which pulse will be emitted along the line 223, noting that the cathode of triode 224 is at a negative 60 volt potential while its anode is connected to a positive 10 volt potential. The circuit of the triode 224 is only sensitive to positive pulses delivered to it through the resistor 222, since it is normally cut-ofi by the negative potential of its grid with respect to its cathode.

As the magnetic tape advances beneath the heads the trailing edge of a pulse will ultimately produce signals which at the grid of tube I8 Will be in phase with the output at the terminal |53. As indicated previously, a negative pulse will thus be produced through the line 92 which will render the triode 202 of the ilip-Iiop 200 nonconducting and the triode 204 conducting. The neon tube 2id will now be fired and a negative pulse will be transmitted through the condenser EIS. This negative pulse, Without eiect on the circuit of triode 22d, will be transmitted to the grid of the triode 234 through condenser 232 and resistor 238, as a sharp pulse due to differentiating action, to cause it to become momentarily non-conducting, interrupting the flow of current to it through the resistor 252, the crystal diode 252 and the line 240.

The circuit element B comprises a iiip-ilop 244 including the triodes 222 and 250 in conventional connections. The line 104 is, .during reading of the tape, connected through the switch 242 to the grid of triode 249. A neon lamp 245 inseries with a resistor 241 is illuminated when ,the tube '25o is conducting.

A negative pulse through the line |04 renders the triode 249 non-conducting and the triode 250 conducting. The line 243 is thus rendered more positive. Less current is accordingly drawn through the resistor 252 and the crystal diode 25d so that the junction of the anodes of the diodes 25B and 253 is no longer prevented from going positive with respect to the cathode of a pentode 260 which is connected to a positive 40 volt source. The control grid of this pentode is connected to the junction just mentioned through a line 254 and resistor 262. At the time the fllpiiop :Efiii shifts as just described the grid of the pentode Zli will remain at practically the same potential as it was previously, due to the current drawn through the diode 256 and line 240. However, when a negative pulse is applied to the grid of the triode 234 and this triode becomes nonconducting the potential at the grid of the pentode 266 becomes positive with respect to its cathode and accordingly the pentode 260 becomes conducting, drawing a large current from the terminal 264 through the switch 266 which is in the position illustrated. As will be described hereafter, this terminal is connected through a solenoid of a corresponding clutch mechanism in the decoding machine of an electric typewriter to a positive 300 volt potential.

The foregoing description has mentioned only single circuit elements A and B. Actually when a multiple channel tape is used there is one of each of these elements present for each channel while there is only one of each of elements C and D in the entire device. In order now to make clear the complete assembly, reference may be made to Figure 2 which shows the interconnections ior a multiple channel device. In Figure 2 there is indicated at E an electrical typewriter capable of encoding to produce magnetic pulses in six channels of a magnetic tape and of decoding signals received from the six channels of a magnetic tape and typing letters, numerals and characters in accordance with the grouping of corresponding pulses in the several channels. The encoding portion of the electric typewriter is indicated at F while the decoding portion is indicated at G.

The typewriter is to a mapor extent (except for Figure 9) merely diagrammed herein since its internal devices are well known and are illusthose illustrated. recognized the various lines interconnecting, and external to, the circuit elements described in detail. As will be noted, the lines 5, 92 and |02 'from the circuit element C connect to all of the 'corresponding lines of attest? 'trated, for example, in the'patents tolFtch et al.

2,161,564, dated June 6, 1939 and 2,165,247, dated July l1, 1939. The former patent illustrates the encoding device of the typewriter and from this it will be evident that depression of a particular :typewriter key will eifect the transmission of pulses on six output channel lines, which pulses, 'as hereinafter described, will provide the mag- -netic pulses in the various channels of the tape.

Thelatter patent illustrates the mechanism by "means of which pulses originating in six channels of a tape will, by the actuation of clutches and associated devices, control the operation of the typewriter to print letters, numerals or characters which correspond to the pulse group on the tape. In the portion G of the diagram there areillustrated a group of solenoids which are connected to a common positive 300 volt potential source and to lines 264 heretofore described.

These solenoids are the clutch controlling solenoids illustrated in Patent 2,165,247.

In Figure 2 there are illustrated the first, sec- A-ond and sixth pairs of circuit elements A and B `with the third, fourth and fth omitted to simplify the diagram. It will, of course, be understood that these are present and are connected into the complete circuit in the same fashion as In Figure 2 there will be the circuit elements A.

The same is true of the lines 84 and 86 from the circuit element D. Lines 228 and 240 from the circuit element C connect with the corresponding lines of the circuit elements B. The corresponding circuit elements A and B of the same channel `are connected by the lines |04 and 261. To the `coils in the decoding portion G in the typewriter 'there extend the lines 264 from the elements B. From the encoding portion F of the typewriter there extend the separate channel lines |05 to `the elements B and also thelines 2|5 and 22| to the element C. -(The last three lines have not yet been discussed.)

LBefore proceeding with the description of the `overall tape reading operation and the operation of the typewriter thereby there will be described `the mechanical and electromechanical elements Vinvolved in reading signals out of the tape and Vin imposing the magnetic pulses thereon. Re-

ferring first to Figures 3 to 7, inclusive, there is illustrated therein the assembly of heads for the various tape channels. Blocks 302, 304 and 306,

' of non-magnetic material such as beryllium-copper, or hard -bronze or brass which will resist `abrasion when in contact with the magnetizable tape, are accurately machined and ground and assembled with shims 334 and 336 of non-magnetic material between them through the use of `bolts 308 and 3|0 and aligning pins 330 and 332.

The adjacent faces of these blocks are ground flat so as to insure close dimensional tolerances. Extensions 3|2- and 3|4 have bolted to their accurately ground side faces guiding discs 3|6 and 3|8 for the tope. Milled slots 320 and 322 are provided in the adjacent faces of the blocks 302 Aand 304, and 304 and 306, respectively. There are also milled out hollows 324 and 326 for the reception of the coils of the heads, the leads from which pass out through openings 325 and 321. Within each of the slots 320 and 322 there are located the stacks of accurately dimensioned 'laminations 338 and 340 which form the magrespond to the coils 2 of the wiring diagram) and interruptions in the continuity of the laminated cores are provided by the shims 334 and 336. These shims may be 0.0001 to 0.001 inch in thickness and define the gaps in the individual heads which are required for both producing magnetization of the tape and for reading out the signals therefrom. To Secure great accuracy, the grinding of the adjacent faces of the blocks may be accomplished with the laminated cores in place.

Between the various slots 320 and 322 there are sawed slots 328 into which there are driven, after assembly, thin sheets of soft iron which prevent cross-talk between adjacent heads. Through the presence of these soft iron shims cross-talk between the heads is reduced to less than 1%,

though, Iwithout them, cross-talk to the extent of 30% would be expected in an arrangement involving eight channels on a tape of 8 millimeter width.

The entire assembly should be made with the greatest attention to dimensional accuracy since on it depends the accuracy of location of the magnetized spots on the tape and the proper reading of signals from these spots. The edge guides 3|0 and 3|8 should have only minute clearances with the edges of the tape so that it cannot move either laterally or in skew fashion with resultant uncertainty of its position relative to the heads. The relationships between the gaps in the heads and these guides must also be very accurately insured.

As will be noted from Figure 3 the heads are divided into two groups of four heads each in order to provide the necessary spacing for the reception of the coils consistent with the recording of the eight channels on a Vary narrow tape. The spacings between the respective gaps located by the shims 334 and 336 of the two sets of heads must also be very accurately insured since, as will be obvious, the pulses which are simultaneously read are not distributed in a single line across the tape but rather along two lines having different spacing. When reference is made herein to aligned pulses or spots on the tape there will be understood that there is signified the group of pulses which are simultaneously produced or read in the operation of the device and which are aligned with the gaps of their respective channel heads even though they are not arranged in a single line across the tape. With wider tapes or less channels, of course, all of the heads might have their gaps arranged side by side in a single transverse line.

Referring now to Figure 8, the head assembly which has just been described is indicated at H. The tape passes beneath this assembly which is rigidly held against Vibration. A tape supply reel 350 has its mounting shaft connected to a motor indicated at 352 which is continuously energized in a direction to take up the tape. A take-up reel 354 is similarly connected to a motor indicated at 35E which is also energized to take up the tape. The tape 344 extending from these reels passes over idler pulleys 360 and 360 about a drive wheel 358 faced with friction material, thence about idler pulleys 362 and 364, and about the curved lower ends of springs 316 and 318 supported at their upper ends on a xed member 314. The lower ends of these spring members 316 and 318 are connected to a tape guide 380 which, in turn, isr connected 13 through a link 382 with the vibratory element of a driver 38d which has a coil energized through the connections 53 and |55 previously described. This driving device 381i may be in the form of a conventional loud speaker drive adapted t vibrate the members 37d, 318 and 38d at a suitable signal frequency such as 200 to 500 cycles per second in the direction of the length of the portion of the tape passing beneath the head H.

A worin Elli driven by a motor 312 drives a wheel S68 connected to the wheel 355 to impart continuous motion to the tape or, if desired, interrupted motion depending upon the nature of the control of the motor SF2. For present purposes, it may be assumed that the motor 312 runs continuously to feed the tape at a suitable linear speed across the head assembly. The motors 352 and 35E merely insure that the tape is properly taken up on the reels and exert only sufficient torque for that purpose.

From the construction described it will be evident that the small loop of tape below the idlers 362 and 351i is alone subject to vibration through the action of the driver 384 and that this vibration is in the direction lengthwise of the tape where it passes the pick-up heads. This vibra,- tion of the tape creates the signal which appears as an alternating current applied to the grid of the input pentode I8.

Since the arrangement does not involve any motion of the pick-up heads the device is substantially free of disturbances due to the magnetic field of the earth or other stray magnetic fields as contrasted with such devices as would involve vibration of the head or modulation of its magnetic circuit which would require a degree of shielding very difficult to obtain in order to suppress to a satisiactory degree noise signals due to ambient magnetic elds. As also pointed out, the input circuit is of a type which removes the influence of any signals below a certain level. As a result, reading out of the tape pulses can be effected in a thoroughly reliable fashion.

There may now be described the overall operation of the system in the matter of operation of the typewriter from the pulse groups in the channels of the tape.

As will be evident from the construction of the head assembly and from the fashion in which pulses are recorded on the tape the pulses which form a particular code group will be presented to the heads approximately simultaneously and, at any rate, in such fashion that the arrival of Aa peat: of any pulse of a group will not precede the arrival of the leading slope of any other pulse of the group. By accurate construction of the head assembly as described this condition may be easily assured and, accordingly, it will be assumed as a condition preexisting for the operation of reading the tap-e now to be described.

Assuming phasinfr consistent with the preceding description (though, of course, an arbitrary 180 phase shift could be used by slight modification of the circuits) the arrival of the leading portion of the first pulse to reach its corresponding channel head will give rise to an input signal at the tube I8 which will be 180 out of phase with the potential of the terminal |53. ln accordance with the preceding description this will cause the emission of negative pulses along the lines |02 and H14. Preceding this, in the flipop 200 the triode 202 Will have been non-conducting and the triode 284 will have been conducting. The negative pulse which is now emitted through the line H32 will cause the triode 284 to become non-conducting and the triode 202 conducting. A positive pulse is thus provided to the grid of triode 224 and a negative pulse is applied from this tube along the line 228 to each nip-flop 244 in the circuit elements B corresponding to the various channels. It may be noted that this pulse is delivered through a diode 229. The purpose of this diode is to allow the nip-flop, upon being pulsed through the crystal, to become free: i. e. the diode permits the pulse to be delivered to the grid of triode 25|) to initiate the flipping action; but once this has started the potential on this grid will not be restrained to assume the potential of the line 228 and it may become more negative than the potential of line 228. This results in faster 'nipping and more positive action. In each of these elements the triode 25) is thus rendered non-conducting and the triode 24S) is rendered conducting. It is to be noted that since the line l02 is connected to all of the elements A the arrival of a pulse as just described in any of the channels will effect only one operation of the nip-flop 200 which, in turn, will eiect clearing of all of the flip-ops 244 to put them in the condition stated, irrespective of their previous conditions. In the case of those nip-flops 2M having non-conducting triodes 25u there will, of course, be no change effected. The conditions existing from a previous pulse group are thus cleared out of the device.

While only the rst pulse emitted through the line I2 effects any action by throwing the flipflop 20B as stated, as the tape advances the leading portions of each of the tape pulses of the group, including the tape pulse which gave the rst output through the line 102, will cause the emission of at least a plurality of negative pulses through the lines HM. Following the clearing the presence of a pulse in any channel will, accordingly, through this line Hill, render in the corresponding flip-flop 25.4 the triode 249 non-conducting and the triode 256 conducting. The result is that the circuit element B corresponding to any channel involving a tape pulse will be set up so that the crystal gating arrangement, through the line 2&8, will be prepared for the reception of a pulse along the line 248 to effect current flow through the tube 26B.

Nothing will now occur until the peak of one of the tape pulses passes b-y the gap in its corresponding head which, as previously assumed, will occur only after all or" the elements B will be set up corresponding to pulses of the group. Following this event there will be produced an inphase signal at the grid of the tube i8. As previously described this will give rise to a negative output pulse along the line 92 to the grid of the triode 2e? causing this tube to become nonconducting and tube 2M to become conducting. A negative pulse is emitted through the condenser 232 producing a cut-01T of tube 23d which, through the lines 249, will result in operation of the gating elements at the input to the tubes 259 in elements B. Accordingly, the tubes 26S which correspond to those channels containing tape pulses will provide current now through the corresponding clutch controlling solenoids G' of the decoding portion G of the electric typewriter. As described in Patent 2,165,247 there is thus produced operation or^ the typewriter key bars to result in the typing of a letter, numeral or other character corresponding to the code group which has been read. It Will be noted that lacaaeoff the' operation of all of the solenoids is effected simultaneously and in accordance with the single signal which is produced by the most advanced peak of the tape pulses in a particular group. It will be evident that subsequent negative pulses delivered through the line 92 will have no eiiect on the nip-flop 200 and the entire system is accordingly restored to the condition assumed existing at the beginning of this description of the tape reading operation.

It may be here noted that condenser 232 differentiates signals fed to it. This provides a time constant sufficiently short so that the brief pulse applied to the tube 23d, while long enough to produce reliable actuation of the clutches by the typewriter receiving solenoids, will nevertheless be short enough to avoid double actuation which would involve printing a character twice. The proper time is provided by the combination of condenser 232 and resistor 236. The condenser 23|, used in recording, has a much larger capacitance than condenser 232 since differentiation is not desired during recording, the timing being obtained from flip-nop 200 when connected as a delay flop.

At this point there may be indicated some typical data which has been found to give excellent results. A satisfactory frequency for the longitudinal vibration or oscillation of the tape has been found to be from 400 to 500 cycles per second. This frequency is sufficiently high so as not to impede or interfere with the operation of the typewriter and to give rise to signals of suincient amplitude to be readily amplified and utilized in the system. On the other hand, the frequency in this range is not too high to give rise to resonant or other difficulties in the mechanical vibrating system. Y

A satisfactory amplitude of vibration of the tape lies in the range of 0.001 to 0.002 inch.

The gaps in the heads may desirably be in the range from 0.0005 to 0.0015 inch. The spacing between pulses along a channel may be about 0.01 inch. The length of a pulse may be of the order of 0.005 inch or less. A linear movement of the tape to correspond to reading of eight pulse groups per second, i. e., a movement of about 0.03 inch per second, has been found very satisfactory with a typewriter capable of operation at moderate speeds.

It is to be understood that the figures just given are those which have been used in a particular instance and are not to be regarded as critical or as restrictive of the invention. With higher speed typewriters, for example, it would be possible to read from the tape a substantially larger number of groups per second and with increased precision of construction of head assemblies and decrease of the head gaps the pulses on the tape may have reduced linear dimensions and may be more closely arranged. Even the conservative figures given, however, will show that a very large number of characters may be represented on a single foot length of tape.

"A, mathematical analysis of the reading oi pulses from an oscillating tape in accordance with the described procedure shows that there are delivered from the head frequency modulated signals and leads to the following conclusions:

The signal output from the tape due to its oscillation increases substantially linearly with oscillation frequency.

The signal output from the tape increases with the amplitude of oscillation but not linearly and reaches a maximum when the amplitude is close i6 to a quarter cycle length of the pulse distribution along the tape.

If only frequencies close to the frequency of oscillation are ultimately passed then the wave shape of the original wave (if non-sinusoidal) is increasingly distorted with increasing amplitude of oscillation.

As will be evident from the foregoing, the circuits which have been described are applicable to a system in which modulation is eifected otherwise than by the oscillation of the tape, for example, by producing varations in the reluctance of magnetic circuits or the like.

1t may also be noted that the system for securing the simultaneous delivery of pulse outputs from a plurality of channels despite possible slight misalignment of the pulses of a group is applicable to the use of a fast moving tape which, without being oscillated, will produce signals of suicient magnitude to produce output pulses which are not submerged in a noise background. The delivery of a number of simultaneous output pulses may be triggered by the passage of the iirst peak of a group in essentially the fashion described.

It will also be evident that this matter of securing a simultaneous output from various channels despite small misalignments of pulses in the channels is applicable not only to magnetic tapes but also to other multiple channel recording as well, for example, such as may be provided photographically on nlm or by punched holes in tapes.

The arrangement by which reading is effected simultaneously from all of a plurality of channels triggered by the attainment of a predetermined condition in any one of them eliminates the necessity for having any sprocket arrangement for triggering the reading operation. Heretofore, for example, if pulses were to be read in groups from six channels, it was necessary to provide either actually or in effect a seventh channel to determine when reading from the six channels should be accomplished. In accordance with the present invention, the sprocketing channel is eliminated altogether. This is accomplished, when n channels are to be read, at no more eX- pense than that of reducing the normally 21L possible pulse groups to 2"1 pulse groups. In other words, the only restriction involved is that there cannot be read that pulse group represented by no pulse in any of the channels. The necessity for this may, of course, be very easily avoided. 4

There is, accordingly, read every group which involves at least one pulse in any channel.

There may now be described the recording of pulses on the tape through the operation of the encoding device F of the typewriter. As will be evident, this result could be accomplished through the use of a circuit entirely independent of the circuit through which reading of the tape is effected, merely switchingthe heads from one circuit to the other as might be required. However, conservation of parts in a complete recording and reading system makes it desirable to utilize as many elements as possible for the tWo purposes and, consequently, in the preferred system which is herein disclosed this is done, the transition from reading the tape to recording on -the tape being accomplished by shifting all of the double-pole switches which are illustrated to their alternative positions. From this point in the description, therefore, it should be understood that such a shift has been effected in the case of each switch.

With the exception of the headvcoils 4and the leads and 261 therefrom the circuit elements A and D are not usedA in the recording operation. There is now no necessity for oscillation of the tape and consequently the circuit element D may, if desired, be taken out of operation through any suitable switching means; however, no harm would be done by oscillating the tape during recording except for a slight lengthening of the recorded pulses. It will be assumed, however, that the tape is advanced at uniform speed past the heads without having oscillations imparted to it.

Assuming the double-throw switches to be in their positions alternative to those illustrated in Figures 1A and 1B and that none of the typewriter keys is depressed the condition of the system will be as follows:

Tube 269 will be cut off due to the low resistance path through the crystal 258, line 24|] and triode 234 to zero potential which causes the grid of tube 299 to be negative with respect to its cathode. Under these conditions the grid of each tube 399 is at cathode potential so that the tube is highly conductive with the result that current hows from the positive 300 volt supply terminal through the tube 30|), line 251, switch 1, terminal 3, corresponding coil 2, terminal 4, common line 5 and switch 235 which now engages contact 231 connected to the positive 220 volt supply terminal. This condition exists in the elements A and B of each channel and accordingly each head has a current continuously flowing through it from its terminal 2 to its terminal 4. Each head is accordingly energized to produce an erasing action on the tape to remove any pulses previously contained thereon and which, as will be pointed out below, are imposed on the tape in a condition of opposite magnetic polarity obtained by current iiow in the opposite direction through the head coils.

The shifting of the switches 29|, 203 and 201 will have transformed the flip-flop 209 into a flip-flop of delay type, i. e., the triode 292 of the ip-op will be normally conducting and the triode 294 normally non-conducting. A negative pulse applied to the grid of the triode 292 will reverse this situation, but only for a limited time after which the flip-flop will return to its original condition. The positive 85 volt terminal from which the anodes of the tubes 22 and 294 are supplied is connected through the adjustable resistor 2|2, resistor 2H and resistor 299 to the anode of the crystal diode 22| which has a return through resistor 2 9 to a positive 10 volt terminal. The anode of the crystal diode is connected to the grid of triode 282 through the switch 293. As will be evident, this means that normally the grid of triode 222 is held positive. The anode of triode 222 is connected through switch 29| and condenser 92 to the junction of resistors 299 and 2| Switch 291 disconnects the grid of triode 294 from line m2 but the grid remains connected to the anode of triode 292 through resistor 206 and also through resistor 223 to minus 60 volts.

As will be pointed out hereafter, negative pulses to throw the flip-flop 229 will be delivered throughy the line 2 E 5 and will be differentiated by the condenser 211 and resistor 2|9 to produce sharp pulses through the crystal diode 22| to the grid of triode 222. When the flip-flop is thus thrown to its abnormal condition it will not return to its normal state until the lapse of a time, period determinedV by the condenser |99 and the resistors 2H and 2| 3. By adustment of the latter thisV time period may be adusted to x the time 18. of application of current for a pulse group thereby determining the lengths of the pulses recorded on the tape.

When the switches are shifted the attainment of the normal condition of the nip-flop 200, i. e., with the tube 264 non-conducting, will have resulted in the application of a positive pulse to the grid of triode 224 which, in the fashion previously described in connection with reading of pulses from the' tape, will result in delivery of a negative pulse to the grid of triode 250 of flip-flop 244 This Flip-flop accordingly will be in a condition in which the triode 249 is conducting and the triode 259 is not conducting. The result is a less positive condition of the line 248 and cathode of crystal diode 258. The tube 26D will accordingly be normally non-conducting as stated previously.

The conditions just described exist when no typewriter key is depressed, and erasing action of pulses from the moving tape occurs.

Reference to Patent 2,161,564 will make clear how depression of a typewriter key will close a selected group of switches to produce current ow through selected ones of six channel lines substantially simultaneously. In Figure 2 these switches are indicated at F' connected to the lines |05. By the key action the lines |05 are thus connected to a bus F which is connected to the line 22|. What occurs may be traced as follows: Starting from the negative. 60 volt potential terminal which is permanently connected to the cathode of triode 224 the circuit may be traced through switch 225, the lter, comprising resistors 221 and 23| andcondenser 223, line 22| and bus bar F". Thence the circuit is completed through the switch contacts F which have been closed by the key operation and lines to the various circuit elements B. In each of these the line |95 connects through resistor |63 and switch 242 to the grid of triode 249. A negative pulse from the negative 60 volt terminal is thus applied to shift the flip-hops 244 corresponding to the channels through which the negative pulses were delivered so that the nip-hops 244 are set up with a resulting more positive condition of the connection 248 of each to the cathode of the crystal diode 258 due to interruption of current ow through triode 249.

As illustrated in Figure 2, there is a seventh contact F connected to the line 2|5 which in the operation of the typewriter is connected to the bus F". The contact just mentioned is not illustrated in Patent 2,161,564 but will be described later with reference to Figure 9. The arrangement is such that movements beyond the closures of the individual line switches connect the line 2|5 to 4the bus, i. e., all of the selected contar-ts at F are completed before the contact at F". contact at F" initiates the pulse effecting record-V ing and by the production of a single pulse insures that the recording starts at precisely the same instant in all of the channels. The action is more precise than dependence upon simultaneity of closure of the various channel switches. Actually these do close very nearly simultaneously and where extreme precision is unnecessary to secure a maximum number of pulse groups per unit length cf tape it will be obvious that the use of a single pulse to initiate recording may be dispensed with, the recording beginning in such case at the time each individual channel switch is closed.

The connection of the line 2| 5 to the bus'results in application of a negative pulse to the differ- As will be immediately described, the

entiating circuit provided by the condenser 2l1 and resistor 2|9 so that a sharp negative P1115@ is applied through crystal diode 22H' to the grid of the tricde 262 of flip-flop 200. The resulting transition of the flip-flop produces a negative pulse through the condenser 23| to the grid of the triode 234. The resulting cutting oif of this triode interrupts current flow through crystal diodes 256 with the result that the grid of each tube 260 corresponding to a channel in which recording is to be effected becomes positive and the tube becomes highly conducting. A circuit through each individual head which is to apply pulses to the tape may now be traced as follows: from the positive 220 volt terminal through contact 231, switch 235, line 5, coil terminal 4, coil 2, terminal 3, switch 1, line 261, resistor 35i and tube 260 to the plus 40 volt supply terminal. The heavy current thus flowing passing through the resistor 30| drives the grid of the tube 305 highly negative with respect to its cathode so that this tube is cut-oil removing in effect the positive 300 volt terminal connected to its anode from the circuit. The current flow just mentioned, it will be noted, is in the direction from the terminal 4 to the terminal 3 of each coil, opposite that previously owing so that now recording will take place. The interval of recording, however, is terminated by the reverse flipping of the nip-flop 2F30 after the pre-set interval. When this occurs negative pulses delivered to the iiip-iiops 244 as above described will clear them to their normal conditions and result in interruption of the recording current flow, reestablishing the erasing current flow by cutting oil tube 268 and again rendering tube 300 conducting. The entire system is thus restored to its initial condition ready for the next operation of a typewriter key.

Figure 9 illustrates the fashion in which provision is made for closing the contact at F" to the line 2|5 previously described. Comparison with the disclosure of Patent 2,161,564 above mentioned will show that the rocking contacts 456 corresponding to those in the patent are provided below their pivots 451 with extensions 455 which are arranged to engage upwardly extending lugs on a slide 41o which is guided for horizontal movement by engagement of screws 412 and 414 within slots 413 and 415. A spring 416 urges the slide toward the left. An insulated extension 480 at the right-hand end cf the slide is arranged to close contacts 41B and i332 having the external connections 484 and 435. As will be evident, whenever any one of the rocking contacts 456 moves counterclockwise the switch contacts 418 and 482 will be closed. If, as usual, two banks of these switches are provided the two corresponding sets of contacts 418 and 482 will be connected in series to provide for a definite single closure of the series circuit. This circuit corresponds to the circuit between the contact involving F'" and the bus F" in Figure 2.

It will be clear from the foregoing that the circuits which have been described are not necessarily limited to recording on or reading from magnetic tape as the record element. As a most obvious variant of the invention there may be cited recording on and reading from photographic nlm in which case pick-up would involve photoelectric devices and recording would involve illumination ofthe film. It will be readily apparent to those skilled in the art how such substitutions may be made for the magnetic heads which have been described.

Furthermore it will be evident that instead of a typewriter as the encoding and decoding device there may be used many other devices, including punched tapes or cards for inserting information into the system and printing or card or tape punch devices or the like for receiving the information from the system.

What we claim and desire to protect by Letters Patent is:

1. In combination, a magnetic member carrying code pulses, a magnetic pick-up device responsive to said code pulses, means for moving said member past said pick-up device to brinsr successive pulses adjacent to said pick-up device, and means for oscillating at least the portion of said member adjacent to said pick-up device to produce alternating signals therein.

2. In combination, a member carrying a plurality oi. channels of code pulses represented by modifications of a physical characteristic of said member, a plurality of pick-up devices responsive to said modifications in said physical characteristic, each responsive to the code pulses of one of said channels, means for moving said member past said pick-up devices to bring successive pulses of the channels adjacent to their respective pick-up devices, and means for oscillating at least the portion of said member adjacent to said pick-up devices to produce alternating signals therein.

3. In combination, a member carrying code pulses in the form of magnetized spots, a head comprising a core having a gap therein and a coil wound. on said core, means for moving said member past said gap to bring successive pulses adjacent to said gap, and means forV oscillating at least the portion of said member adjacent to said gap to produce in said coil alternating signals when arpulse is adjacent to said gap.V

4. In combination, a member carrying a plurality of channels of code pulses in the form of magnetized spots, a plurality of heads corresponding to said channels and each comprising a core having a gap therein and a coil wound on said core, means for moving said member past said heads to bring successive pulses in the channels adjacent to their corresponding gaps, and means for oscillating at least the portion of said member adjacent to said gaps to produce in said coils alternating signals when pulses are adjacent to said gaps.

5. In combination, a member carrying code pulses in the form of magnetized spots, a stationary pick-up device comprising a core having a gap therein and a coil wound on said core, and means for moving said member past said gap with a velocity which may be expressed as the sum of an essentially nonperiodic function of time Yand a periodic function of time.

6. In combination, a member carrying a plurality of channels of code pulses in the form of magnetized spots, a plurality of normally stationary heads corresponding to said channels and each comprising a core having a gap therein and a coil wound on said core, means for moving said member past said heads with said channels substantially in alignment with said heads and with a velocity which may be expressed as the sum of an essentially nonperiodic function of time and a periodic function of time.

7. In combination, a sensing head, means for advancing a magnetic record member pa-st said sensing head, means for oscillating said member in the vicinity of said sensing head so that pulses on the member will produce oscillating signals from said head, a phase detector receiving signals from said head and from said oscillating 21l means. and providing alternative signals depending upon the relationship of phase of thesignals received thereby from the head and oscillating means, and means controlled by said alternative signals to emit a signal when a predetermined change of said phase relationship occurs.

8. In combination, a sensing head, means for advancing a magnetic record memberl past. said sensing head, means for oscillating said member in the vicinity of said sensing head so that pulses on the member will produce oscillating signals from said head, vand phase sensitivey means for emittingv a signal when there occurs a predetermined change of phase relationship between said member oscillating meansv and thesignals from said head.

9.Y In combination, a sensing head, meansfor advancing a magnetic record member past said sensing head, means for producing oscillations oi said member in the vicinity of said head so that pulses on the member will produce oscillating signa-ls from said head, Iand phasel sensitive means for emitting a signa-1 when there occursa predetermined change of phase relationship between the oscillations of said member and the signals from said head.

10. In combination, a sensing head, means for advancing a magnetic record member past said sensing head, -cyclically operating modulating means for producing oscillating signals from sai-d head whenpulses on said member-areY located to be sensed by said head, and phase sensitive means for emitting a signal when there occurs a predetermined change of phase relationship between the oscillations of said modulating means and the signals from said head.

1.1. In combination, a sensing head, means for advancing a magnetic record member past said sensing, head, cyclically operating modulating means for producing oscillating signals from said head when pulses on said member are located to bey sensed by said head, and phase sensitive means receiving signals from said modulating means and said head and providing alternative signals depending upon the relationship of phase of the signals received thereby from the modulating means and from said head.

12'. In combination, la plurality of sensing heads, means for advancing past said heads a magnetic tape carrying pulses ina plurality of channels individually. corresponding to said heads,l cyclically operating modulating means :for prqducingfrom` said heads oscillatingsignals when pulses on said tape are located to be sensed by: said heads, phase sensitive means receiving signals from said modulating means and from sai-d heads and providing alternative signals depending upon the relationship of phase ofthe signals received thereby from the modulating means and from said head, means individual to said channels arranged to be set up when one Itype of said alternative signals is provided by' said phase sensitive means, and means cooperating with the last mentioned means for emitting simultaneously signals corresponding to the individual channels when lany signal of the other type is provided by said phase sensitive means.

13. In combination, a plurality of sensing hea-ds, means for advancing past said heads a magnetic tape carrying pulses in a plurality of channels individu-ally corresponding to said `heads, cyclically operating modul-ating means for producing from said heads oscillating signals when pulses on sai-d tape are located to be'sensed by said heads, phase sensitive. means receiving.

signals from saidl modulating means; andA from said heads and providing alternative signals de.- pending upon the relationship of phase of the signalsY receivedl thereby from the modulating means and from said head, means, individual to said -channels arranged to be set up when one type of said alternative signals is provided by said phase sensitivemeans, and means cooperating With the last mentioned meansfor emitting signals corresponding to the individual channels when any signal of the other type is provided by said phase sensitive means.

14. InY combination, a plurality of sensing heads, means, for `advancing past said heads a magnetic tape carrying pulses in a plurality of channels individually corresponding to said heads, cyclically operating modulating means; for producing from said heads oscillating signalsY when pulses on said tape are located to be sensed bysaid heads, said modulating' means oscillating the tape in the vicinity of said heads, phase sensitive means receiving signals from said modulating means and from said heads and providing 'alternative signa-ls depending upon the relationship of phase of the sign-als received thereby from the modulating means and from sai-d head, means individual to said channels arranged to be set up when one type of said alternative signals is provided by said phase sensitive means, and means cooperating with the last mentioned means for emitting simultaneously signals corresponding to the individual channels when any signal of the other type is provided by said phase sensitive means.

l5. In combination, a plurality of sensing heads, means for `advancing past said heads a magnetic tape carrying pulses in a plurality of channels individually corresponding to said heads, cyolically operating modulating means for producing from said heads oscillating signals when pulses on said tape are located to be sensed by said heads, said modulating means oscillating the tape in the vicinity of said heads, phase sensitive means receiving signals from said modulating means and from said heads and providing alternative signals depending upon the relationship of phase of the signals received thereby from the modulating means and from :said head, means individual to said channels `arranged to be set up when onev type of said alternative signals is provided by said phase sensitive means, and means cooperating with the last mentioned means for emitting signals corresponding to the individual channels when any signal of the other type is provided byy said phase sensitive means.

16. In combination, a plurality of sensing heads, means for advancing past said sensing heads ra magnetic tape carrying pulses in a plurality of channels individually corresponding to said heads, cyclically operating modulating means for producing from said heads oscillating signals when pulses on said tape are located to be sensed by said heads, and phase sensitive means for emitting simultaneously signals corresponding individually to said channels lwhen there occurs a predetermined phase relationship between the modulating means and the signals from any one or said heads.

1'7. In combination,y a plurality of sensing heads, means for advancing past said sensing heads a magnetic tape carrying pulses in a plurality of channels individually corresponding to said heads, cyclically operating modulating meansl for producing from said heads oscillating signals when pulses .on saidtape-arelocatedto be Y Y sensed by said heads, and phase sensitive means for emitting signals corresponding individually to said channels when there occurs a predetermined phase relationship between the modulating means and the signals from any one of said heads.

18. In combination, a plurality of sensing heads, means for advancing past said sensing heads a magnetic tape carrying pulses in a plurality of channels individually corresponding to said heads, cyclically operating modulating means for producing from said heads oscillating signals when pulses on said tape are located to be sensed by said heads, said modulating means oscillating the tape in the vicinity of said heads, and phase sensitive means for emitting vsimultaneously signals corresponding individually7 to said channels when there occurs a predetermined phase relationship between the modulating means and the signals from any one of said heads.

19. In combination, a plurality of sensing heads, means for advancingpast said sensing heads a magnetic tape carrying pulses in a plurality of channels individually corresponding to said heads, cyclically operating modulating means for producing from said heads oscillating signals when pulses en said tape are located to be sensed by said heads, said modulating means oscillating the tape in the vicinity of .said heads, and phase sensitive meansfor emitting signals corresponding individually to said channels when there "occurs a predetermined phase relationship between the modulating means and the signals from any one of said heads.

20. In combination, a plurality of sensing heads, means for advancing past said sensing heads a magnetic tape carrying pulses in a plurality of channels corresponding to said heads, the pulses being arranged in groups so that a plurality of pulses in diiferent channels may reach their sensing heads approximately simultaneously, control means developing control stimuli governed by the relative displacement between sensing head and associated pulses in each of said channels, and means connected with said control means and said sensing heads for emitting signals corresponding to sensed pulses of a group in response to said control stimuli.

21. In combination, a plurality of sensing heads, means for advancing past said sensing heads a magnetic tape carrying pulses in a plurality oichannels corresponding to said heads, the pulses being arranged in groups so that a plurality of pulses in different channels may reach their sensing heads approximately simultaneously, and means for emitting simultaneously signals corresponding to sensed pulses of a group when the peak of any one of the pulses of the group passes the position of sensing relationship with its head.

22. In combination, a plurality of sensing devices, means for advancing past said sensing devices a strip carrying pulses in a plurality of channels corresponding to said devices, the pulses being arranged in groups so that a plurality of pulses in different channels may reach their devices approximately simultaneously, control means developing control stimuli governed by the relative displacement between sensing head and associated pulses in at least one of said channels, and means connected with said control means and a plurality of said sensing devices for emitting signals corresponding to sensed pulses of a group in response to said control stimuli.

23. In combination, a plurality of sensing de. vices, means for advancing past said sensing devices a strip carrying pulses in a plurality of channels corresponding to said devices, the pulses being arranged in groups so that a plurality of pulses in different channels may reach their devices approximately simultaneously, and means for emitting simultaneously signals corresponding to sensed pulses of a group when the peal: of any one of the pulses of the group passes the position of sensing relationship with its device.

24. In combination, a pair of blocks having plane faces adjacent to each other, a strip of thin non-magnetitc material between and spacing said plane faces, slots in the plane faces of the blocks in alignment across said strip, laminated core assemblies in said slots having gaps provided by said strip, windings on said core assemblies, and means for guiding a magnetic tape across said gaps.

25. In combination, a pair of blocks having plane faces adjacent to each other, a strip of thin non-magnetic material between and spacing said plane faces, slots in the plane faces of the blocks in alignment across said strip, laminated core assemblies in said slots having gaps provided by said strip, windings on said core assemblies, slits located between said slots in the plane faces of the blocks and in the strip therebetween, magnetic shielding strips in said slits, and means for guiding a magnetic tape across said gaps.

26. In combination, an intelligence bearing medium, a normally stationary pick-up device operatively associated therewith, driving apparatus relatively displacing said medium past said pick-up with a displacement characteristic representing the sum of a substantially linear time function and a periodic time unction, and means adapted to receive the output of said pick-up device.

27. In combination, a normally stationary pick-up device adapted for cooperation with an intelligence bearing medium, driving apparatus adapted to relatively displace said medium past said pick-up with a displacement characteristic representing the sum of a first non-periodic time function and a second periodic time function, and means for deriving signals from said pick-up device.

28. In a magnetic sensing device, a supporting member provided with rst and second essentially planar slots and aA third essentially planar slot intermediate said rst and second slots, iirstand second electromagnetic transducers disposed at least partially Within said nrst and second slots, and a paramagnetic member disposed within said third slot.Y

29. In a magnetic sensing device, a rst supporting member having a first set of slots in one of its faces and a second set of relatively staggered slots in another of its faces, a second supporting member maintained in intimate relationship with a rst slotted face of said first supporting member and provided with a set of slots matching and registering with the slots in the adjacent face of said first supporting member, a third supporting member maintained in intimate relationship with another slotted face of said first supporting member and provided with a set of slots matching and registering with the slots in said other slotted face, and electromagnetic transducers disposed within said slots.

30. In a magnetic sensing device, a iirst supporting member having a rst set of slots in one of its faces and a second set of relatively' staggered slots in another of its faces, a second supporting member maintained in intimate relationship with a rst slotted face of said rst supporting member and provided with a set of slots matching and registering with the slots in said rst slotted face of said first supporting member, a third supporting member maintained in intimate relationship with a second slotted face of said first supporting member and provided with a set of slots matching and registering with the slots in said second slotted face, electromagnetic transducers disposed within said slots, shield receiving slots disposed intermediate said transducer receiving slots, and paramagnetic shields disposed within said shield receiving slots.

31. In combination, a plurality of sensing heads, means for advancing past said sensing heads a magnetic member carrying pulses in a plurality of channels corresponding to said heads, the pulses being arranged in groups so that a plurality of pulses in diierent channels may reach their sensing heads approximately simultaneously, control means developing control stimuli governed by the relative displacement between sensing head and associated pulses in at least one of said plurality of channels, and means connected with said control means and a plurality of said sensing heads for emitting signals corresponding to sensed pulses of a group in response to said control stimuli.

JOHN PRESPER ECKERT, J R.

JOHN C. SIMS, JR.

HERBERT FRAZER WELSH.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,419,256 Hammond June 13, 1922 1,848,799 Papalia Mar. 8, 1932 2,158,285 Koch May 15, 1939 2,229,326 Heller Jan. 21, 1941 2,300,463 Palme Nov. 3, 1942 2,403,009 McCann July 2, 1946 2,423,339 Newman July l, 1947 2,424,295 Williams July 22, 1947 

